Archives For safety cases

Safety case notes

08/04/2016

Update to the safety case module of my UNSW course. Just added a little bit more on how to structure a physical safety case report.

Just updated the course notes for safety cases and argument to include more on how to represent safety cases if you are not graphically inclined. All in preparation for the next system safety course in July 2016 at ADFA places still open folk! A tip o’ the hat to Chris Holloway whose work prompted the additional material. 🙂

Midlands hotel

A quick report from sunny Manchester, where I’m attending the IET’s annual combined conference on system safety and cyber security. Day one of the conference proper and I got to be lead off with the first keynote. I was thinking about getting everyone to do some Tai Chii to limber up (maybe next year). Thanks once again to Dr Carl Sandom for inviting me over, it was a pleasure. I just hope the audience felt the same way. 🙂

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…and the value of virtuous witnesses

I have to say that I’ve never been terribly impressed with ISO 61508, given it purports to be so arcane that it require a priesthood of independent safety assessors to reliably interpret and sanction its implementation. My view is if your standard is that difficult then you need to rewrite the standard.

Which is where I would have parked my unhappiness with the general 61508 concept of an ISA, until I remembered a paper written by John Downer on how the FAA regulates the aerospace sector. Within the FAA’s regulatory framework there exists an analog to the ISA role, in the form of what are called Designated Engineering Representatives or DERs. In a similar independent sign-off role to the ISAs, DERs are paid by the company they work for to carry out a certifying function on behalf of the FAA.

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Well it sounded reasonable…

One of the things that’s concerned me for a while is the potentially malign narrative power of a published safety case. For those unfamiliar with the term, a safety case can be defined as a structured argument supported by a body of evidence that provides a compelling, comprehensible and valid case that a system is safe for a given application in a given environment. And I have not yet read a safety case that didn’t purport to be exactly that.

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The development of safety cases for complex safety critical systems

So what is a safety case? The term has achieved an almost quasi-religious status amongst safety practitioners, with it’s fair share of true believers and heretics. But if you’ve been given the job of preparing or reviewing a safety case what’s the next step?

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Recently there’s been some robust discussion over on the Safety Critical Mail List at York regarding the utility of safety cases and performance based safety standards (as exemplified by the UK safety case regime) versus more prescriptive design standards (as exemplified by the aerospace industry FAR regulations). To provide one UK regulator’s perspective here’s a presentation by Taf Powell, Director of the Offshore Division of Health and Safety Executive’s Hazardous Industries Directorate, UK, on the state of safety cases in the UK offshore industry circa 2005. Of course his talk was well before the 2010 Deepwater Horizon disaster.

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